The present invention relates to a steam turbine having a turbine casing in which two or more of turbine pressure sections including a high pressure turbine section, an intermediate pressure turbine section and a low pressure turbine section are combined and accommodated.
In a conventional steam turbine, in order to a increase an output power thereof, a turbine casing thereof is divided into a high pressure turbine casing, an intermediate pressure turbine casing and a low pressure turbine casing, and a turbine rotor (turbine shaft) including a turbine nozzle and a turbine movable blade is accommodated in each of the casings, thereby constituting a high pressure turbine section, an intermediate pressure turbine section and a low pressure turbine section. The conventional steam turbine is operated as a so-called power train in which the shafts of the turbine rotors of the high, intermediate and low pressure turbine sections are connected to one another in a form of a train.
If the high, intermediate and low pressure turbine sections are disposed as the power train, the steam turbine takes a span as long as at least about 30 m although depending upon the output power thereof. Therefore, there has been realized a so-called high-low pressure integrated type turbine or high-intermediate pressure integrated type turbine in which two or more of the high, intermediate and low pressure turbine sections are combined and accommodated in one casing so as to shorten the span.
If the steam turbine is the high-low pressure integrated type turbine or the high-intermediate pressure integrated type turbine, the turbine rotor thereof must inevitably handle many kinds of steams having different temperatures. However, recently, there has been realized a high-low pressure integrated type turbine or a high-intermediate pressure integrated type turbine in which a portion of one turbine rotor exposed to steam having high pressure and high temperature under different thermal treatment conditions is provided with high temperature strength and another portion thereof exposed to steam having relatively low pressure and low temperature is provided with tensile strength and low temperature toughness. Such a high-low pressure integrated type turbine or a high-intermediate pressure integrated type turbine has showed a number of good experience records.
Further, in a recent thermal power plant, there have been realized a number of combined cycle power plants in which steam turbine and exhaust heat recovery means are combined in a gas turbine instead of a conventional power plant.
A steam turbine employed in this combined cycle power plant is used in a condition that as the steam turbine, one having output of 100 MW is selected in view of current state of the gas turbine output of 100 MW, a steam pressure is set to 100 kg/cm2, a steam temperature is set to 500xc2x0 C., a height of a turbine movable blade of the final stage of the low pressure turbine is set to 36 inches or more in a region of 50 Hz at 3,000 rpm, and the height is set to 33.5 inches or more in a region of 60 Hz at 3,600 rpm. In this case, the steam turbine is formed into a so-called uniaxial type turbine in which a steam turbine shaft is directly connected to the gas turbine. Therefore, a high-low pressure integrated type turbine or a high-intermediate pressure integrated type turbine is employed as the steam turbine, thereby shortening a span between bearings and reducing an installation area.
As described above, in the combined cycle power plant going mainstream in place of the conventional power plant, the number of shafts of the gas turbines directly connected to the steam turbines is set to five or more so that a total output power becomes 1,000 MW or greater, the steam turbine is formed into the high-low pressure integrated type turbine or the high-intermediate-low pressure integrated type turbine, so that an installation area of the five shaft arrangement is further reduced to effectively utilize a site or land.
In a recent thermal power plant, one of the high-low pressure integrated type turbine and the high-intermediate-low pressure integrated type turbine is selected as a steam turbine used in the combined cycle power plant, thereby further reducing the installation area. However, there still exist the following problems:
(1) In a steam turbine provided with one turbine rotor, the turbine rotor includes a high-intermediate-low pressure section or a high-low pressure section, a high-intermediate pressure section is provided with high temperature strength (creep strength) and a low pressure section is provided with high tensile strength and high toughness. Such a steam turbine is already on its way to reaching limitations to simultaneously satisfy the mutually contradictory functions of high temperature strength, the high tensile strength and the like and to further increase such strength. That is, when attempt is made to further increase a volume of a single steam turbine, it is inevitably necessary to increase the temperature of steam and to increase the length of the turbine blade. However, in the case of the turbine rotor including the conventional high-intermediate-low pressure section or the high-low pressure section, it is difficult to sufficiently secure the strength including high temperature strength and vibration strength. For this reason, a countermeasure is required to secure the strength of the turbine rotor to counter the high temperature of steam.
(2) When thermal treating temperatures of the high-intermediate pressure section and the low pressure section are changed from each other so as to provide the high-intermediate section or the high pressure section with high temperature strength and to provide the low pressure section with tensile strength and toughness, a gap is provided between the high-intermediate pressure section and the low pressure section. Moreover, a partition plate is provided in the gap, and temperature gradient thermal treatment is carried out. However, in a case where radius of curvature of a groove bottom (heat groove, hereinafter) of the gap is small, there is a problem that quench crack is generated in the turbine rotor at the time of the temperature gradient thermal treatment.
(3) When the temperature gradient thermal treatment is carried out in a condition that the gap is formed between the high-intermediate pressure section and the low pressure section and the partition plate is provided in the gap, if the steam temperature at a position where the partition plate is disposed is 400xc2x0 C. or more, the high temperature strength of the high-intermediate pressure section after the thermal treatment is not sufficient and the high temperature toughness is insufficient, being defective and inconvenient.
(4) When the high-intermediate pressure section and the like and the low pressure section are subjected to the temperature gradient thermal treatment, since it is necessary to secure a place where the partition plate is disposed, the turbine rotor is provided with the gap, and this inevitably increases the span of the turbine rotor. Therefore, at a time of securing the position to dispose the partition plate, it is necessary to shorten the span of the turbine rotor to secure the place where the partition plate is disposed.
The present invention has been accomplished in view of the above circumstances, and it is an object of the present invention to provide a steam turbine capable of sufficiently securing strength of a turbine rotor including a high-intermediate-low pressure section or a high-low pressure section against high temperature of steam and long length of a turbine blade in accordance with increasing of volume of a single device.
This and other objects can be achieved according to the present invention by providing a steam turbine including a turbine high pressure section, a turbine intermediate pressure section and a turbine low pressure section, in which at least two or more of the pressure sections are combined together, and a turbine rotor which is subjected to a gradient thermal treatment at different thermal treating temperatures at respective pressure sections is rotatably supported by bearings and accommodated in a turbine casing, and in the improvement of the steam turbine, in a case where an axial distance from a setting position of a turbine movable blade of a final stage of the turbine low pressure section to a setting position of a partition plate disposed at a time when the gradient thermal treatment is performed to each of the pressure sections at different thermal treating temperature is defined as A, a blade length of the turbine movable blade is defined as B, and an axial distance from a prior stage of the final stage of the turbine low pressure section to the setting position of the partition plate is defined as C, the setting position of the partition plate is set in a range of (A/B)xe2x89xa70.9 and Cxe2x89xa7300 mm.
In preferred embodiments in the above aspect, a gap of the turbine rotor in which the partition plate is disposed is defined as H and a radius of curvature of a groove bottom of the gap is defined as R, the gap H and the radius R of curvature of the groove bottom are set in ranges of Hxe2x89xa7140 mm and Rxe2x89xa770 mm.
The partition plate is disposed at a position at which a steam temperature is 400xc2x0 C. or less.
The partition plate is disposed at a position of either one of space regions of a low pressure steam inlet and a low pressure bleeder port of the turbine low pressure section.
In a case where a bearing span of the turbine rotor is defined as L, the bearing span L is set in a range of Lxe2x89xa75,700 mm.
A blade length of the turbine movable blade in the final stage of the turbine low pressure section is 30 inches or more.
At least one of the turbine sections is supplied with a steam having pressure of 100 kg/cm2 or more and temperature of 500xc2x0 C.
As described above, according to the steam turbine of the present invention, when the turbine high-intermediate pressure section and the turbine low pressure section, or the turbine high pressure section and the turbine low pressure section of the turbine rotor are subjected to the gradient thermal treatment at different temperatures, a setting position of the final stage of the turbine low pressure section is taken as a reference, a blade length of the turbine movable blade in the final stage, an axial distance from the final stage to the setting position of the partition plate for the gradient thermal treatment, and an axial distance from the second stage from the final stage to the setting position of the partition plate for the gradient thermal treatment are taken into consideration comprehensively to set a proper position of the partition plate for the gradient thermal treatment. Therefore, a high temperature strength can be secured by the turbine high-intermediate pressure section or the turbine high pressure section, high tensile strength and toughness can be secured by the turbine low pressure section. It is therefore possible to sufficiently cope with high temperature tendency of a single device volume and high output tendency.
Furthermore, according to the steam turbine of the present invention, since the bearing span is set to appropriate position so that the rated rotation number of the turbine rotor can be detuned sufficiently highly from the critical speed region, it is possible to allow the turbine rotor to operate safely and stably.
The nature and further characteristic features of the present invention will be made more clear from the following descriptions made with reference to the accompanying drawings.